Figure 2.

Schematic representation of the Double Sensor building blocks and core body temperature (CBT) estimation principles. The Double Sensor is composed by two temperature sensors (black dots), measuring temperatures T₁ (approximating skin temperature T_skin) and T₂ (approximating ambient temperature T_amb), respectively, which are separated by a disk of insulating material (in blue) of known heat transfer coefficient K_s. Neglecting heat flux through lateral walls (dashed arrows), CBT can be estimated simply equating the heat flux from the body to the skin (with body heat transfer coefficient K_g) to the heat flux from the skin through the sensor (red arrows), leading to the equation on the right.